Endothelin-1 is a potent vasoconstrictor and binds to two receptors, ET-A and ET-B, which are variable expressed on endothelial cells, smooth muscle cells, and fibroblasts. Furthermore, endothelin-1 has been found to be released in vitro by scleroderma fibroblasts and could contribute to the development of dermal fibrosis in systemic sclerosis. Bosentan is a dual receptor antagonist, that competes with the binding of endothelin-1 to both receptors and has already been approved for the treatment of pulmonary arterial hypertension in Europe, the US, and some other countries. The purpose of this study is to evaluate the effect of bosentan treatment on skin fibrosis and functionality in patients with systemic sclerosis.